The use of fingerprints and palm prints are widely employed to identify individuals. It is common to ink both fingerprints and palm prints and apply a print to a card. The inked cards are then sent to forensic laboratories where they can be scanned into a computer and used for comparison to fingerprints or palm prints already in the computer. Often times the inked images are rejected by forensic laboratories because of poor quality. If an inked card is rejected, the prints need to be redone. The process of inking prints and rejecting cards is very costly.
Electronic techniques have been developed to optically scan fingerprints into computers. By optically scanning fingerprints into a computer, the quality of the prints may be assured. Commercially successful techniques of optically scanning fingerprints employ a prism on which a finger is rolled. Commonly assigned U.S. Pat. No. 4,933,976 teaches that a camera can continuously take photos of a finger rolling across a prism and that those photos may be merged together as a mathematical function of their overlapping portions to form a composite image of a rolled fingerprint. In practice the prism provides a generally flat surface and the photos are taken by a CCD element.
Palm print devices, however, have not been commercially successful. One reason might be that the use of a prism to capture palm prints creates problems. One of the problems is that the use of prisms to capture images creates parallax. To capture a satisfactory palm image, at resolutions mandated by government agencies using the technique taught by the '976 patent would require very intense light source and an extremely large CCD element. In practice while such components are available in the market place they are not commercially viable due to their cost, and energy requirements.
One attempt to capture palm print images is described in U.S. Pat. No. 5,528,355 to Maase. Maase discloses a system which utilizes a prism having a curved portion and an adjacent flat portion. The palm is placed on the curved portion with the heel of the palm being on the flat portion of the prism. According to the disclosure in Maase, the curved surface of the prism permits more constant contact between the palm and the prism thereby providing an improved palm print image. Maase does not address the problem associated with parallax and thus does not provide an accurate palm print image.
Therefore a need exists to provide an improved palm scanner.